Multiple telephony



Dec. 11, 1928' E. RUHMEIFZ.

HULTZPLE TELEPHONY Original Filed April 1, 1911 m i R, v. mwm M Mi i mu n w WW4 a Reissued Dec. 11, 192s.

Re., 17,15s

UNITED STATES PATENT OFFICE. 4

ERNST BUHMER, DECEASED, LATE OF BERLIN, GERMANY, BY EDWIN GRUHL, AS-

SIGNEE, OF NEW YORK, N. Y., ASSIGNOR '10 WIRED H. Y., A OOBPORATION OF DELAWARE.

RADIO, INCL, OF NEW YORK,

MULTIPLE TELEPHONY." r

I Original application filed April 4, 1911, Serial No. 618,871, and in France April 5, 1910. Renewed Y February 4, 1919, Serial No. 275,001. Original No. 1,356,222, dated October 19, 1920. Application or reissue filed February 21, 1925. Serial Ila-10,983.

This invention relates to a method and means by which it is possible to transmit simultaneously several telephonic messages by one and the same transmission line.

5 For transmitting conversations, as in wireless telephony by means of electric waves, alternating currents of high frequency and of different frequencies are used which are superimposed on the line and are separated only at the receiving station, Where they act on different oscillatory circuits tuned with the corresponding oscillatory transmission circuits communicating with the receiving apparatus.

In systems in accordance with this invention comparatively loose coupling is preferably used for connecting the transmission line to the different receiving circuits for the purpose of obtaining perfect separation of the several carrier frequencies, thereby avoiding interference between simultaneous ly transmitted messages or the reception of signals at stations for which they are not' intended.

Prior to this invention it has been proposed to accomplish'multiplex telephony by means of a pluralityof high frequency carrier currents superimposed on a metallic transmission line, but in so far as it has been possible to ascertain, none of the previous attempts was successful because of the fact that no means were provided at the receiving stations,,for rectifying the high frequency carrier urrents-a procedure which has been found to be absolutely essential to the practical operation of such systems. i

The essence of the present invention, therev receiving apparatus at the several stations to the commontransmission line, and second, in

"' providing at each receiving station suitable means for rectifying the received car rier frequencies whereby it is rendered possible to translate the modulated carrier current into audible signals. v Afurther feature of the invention consists in the provision of a'novel device whereby the transmitting and receiving apparatus at each station may be alternately associated with the common'transmission line'and whereby 'theinductive coupling between the line and the transmitting and receiving apparatus may be automatically shifted simultaneously with the switching-over operation.

Several arrangements according to this invention are illustrated by way ofexample in the accompanying drawings, in which:

Fig. 1 is a diagrammatic view representing the transmitting and receiving stations with independent sources of high frequency currents at each transmission station;

Fig; 2 represents diagrammatically a modified form of the improved system;

Fig. 3 shows a combined sending and receiving station embodying the invention.

In Fig. 1, A B C and A B C are and receiving stations. x

For producing high frequency currents a high frequency generator is provided at each respectively the corresponding transmitting transmitting station, as, for instance, an arc 9 with oscillating circuit 0 Z in parallel therewith. The different oscillatory circuits are adjusted, to different frequencies by a proper choice of values of capacitance and inductance respectively for the condenser 0 Modulation of the carrier currents may be effected directly or the supply current may 'be modulated before it reaches the arc; in fore, consists, .first, in loosely coupling the that the microphones at one transmitting station cannot-affect any 'of the carrier current other'than that with which it is individually associated.

In the embodiments of the invention illustrated there-are in each case-an equal number of transmitting stations and receiving stations operatively associated with the same transmission line. Each transmitting station is arranged for communication with one of the receiving stations. I Fig. 1, A B and G are receiving stations each including an oscillatory clrcuit Z tuned to the frequency of the correspond in% transmitting stations A,, B C

ach receiving station includes in additionto tlfe'oscillatory circuit Z 0 a detector (1, thevfunction of which is to rectify the received signal currents as in wireless telephony employing electromagnetic waves, telephones t and condenser lg shunted across the telephones. At station C reception is effected bythe telephone w, which is operated by means of Foucalt currents, no rectifying detector being employed. This latter arrangement while operable, is not entirely weak, but is shown merely as illustrating an satisfactory, as the response is extremely alternative possibility.

The coupling of the common transmission line to the transmitting circuits may be comparatively close, but on the contrary the couplingto the receiving circuits must be comparativelyloose.

'relates to an arrangement bymeans of which it is possible to use the s ame oscillatory cir-' cuit atone time as a transmitter and another tlme as a rece ver, so that it is possible to talk and listen alternately with one and the same apparatus. This result is obtained owin to. a commutator or switch S, which sWItchesintO the oscillatory circuit either the I microphone m and the battery in series therewith or the'dete'cto'r d and the telephone t. This switch can be designed so as to al-- 'low' at the same time of a change of coupling of the self-induction coil l withthe line so that when talking there is produced a tighter coupling and when listening a looser couplin This is effected by connecting switch .by means of rod 1' with one arm of bell crank or bent lever g, and connecting the other arm of (1b means of rod 17 with pivoted arm a to which is attached coil 1.

Having now particularly described and ascertained' the nature of the said invention and in what manner the same is to be performed, it is declared that-what'is claimed 1. The combination with 'a conductor, of

, connect either sai nection.

result of such connection;

raise transmission means coupled thereto for im-.

pressing electric oscillations thereon, receiving means associated ,with said transmission means, and shifting means operative to place either said transmission means or said receiving means into operative relation to said conductor andto simultaneously modify the coupling between said conductor and said transmission means.v

. 2. The combination with a conductor provided' with a coil, of a coil inductively re- I lated to and movable with respect to said first mentioned coil, transmission'means for impressing electric oscillations'on said second mentioned coil, receiving means for receiving electric oscillations from said second mentioned coiland means operative to "transmission means or,

said receiving means operatively to said second mentioned coil and to vary the distance between said coils as a result of such con-' 1 '3. The combination vided with a coil, of a coil inductively. related to and movable with respect to. said first mentioned coil, transmission means including a microphone for impressing electric oscillations .onsaid second mentioned coil, receivin'g means-includin a telephone and a detector for receiving efiactric oscillations from said secondmentioned coil, 'an'd means operativeto connect either said transmission means or said receiving means operatively to said second mentioned coil and to vary the distance between said coils as a 4. The combination with means spaced from but. inductively connected to said conductor, transmision means for impressing electric oscillationsvon said first mentioned means, receiving means for receiving electric oscillations from said first mentioned means, and means operative to with a condlictor proa conductor, of U connect either said transmission means or said receiving means operatively to said first mentioned means and to simultaneously and automatically vary the distance betweensaid' conductor and said first mentioned means.

5. The combination with a conductor, of

means. spaced from but inductively connected to sa1 d conductor, transmlsslon means for impressing electric oscillations on said first mentioned means, receiving means for receiving electric oscillations from said first mentioned means, and switching means operative to connect either 'said transmission means or said receiving means operatively to said first mentioned means and to simultaneously and automaticallyvary the distance between said conductor and said first mentioned,

means.

6. In a system ofmultiplextelephony, a

plurality of stations having both transmitting and receiving ap aratus',a common line circuit, means couple to said linecircuit for impressing electric oscillations of difi'erent operative connection with the common line frequencies upon said line circuit, means for circuit, and for simultaneously changing the modifying said electric oscillations by sound coupling between said local circuits and the 10 Waves, local circuits at each station tuned to common line circuit. 5 a particular frequency of said electric oscillations, and means for placing either the EDWIN GRUHL, transmit-ting or thereceiving apparatus in Assignee ofErnst Rukmer, Deceased. 

